The invention relates to a record carrier suitable to be scanned by means of a single scanning head and provided with at least two substantially parallel information layers. Each information layer may comprise information independently of the information contents of other information layers. The information layers may coincide or be separated from each other by a spacer layer. The invention also relates to a scanning device for scanning such a record carrier. During scanning, information can be written, read or erased.
A record carrier of the type described above is known from U.S. Pat. No. 3,855,426. The known record carrier comprises two or more information layers which are separated by spacer layers. An optical scanning device provided with a single scanning head can read one of the information layers by scanning the layer by means of a focused radiation beam from the scanning head. A subjacent or superjacent information layer can be read by means of the same radiation beam by displacing the focus of the radiation beam in a direction perpendicular to the information layer and by positioning it on the desired layer. Due to this mode of serial reading, the collection of information layers in the record carrier can be regarded as a single uninterrupted information area. This is in contrast to a multilayer record carrier which has a scanning head for each information layer. The information areas of the information layers are then read in parallel and should be regarded as separate areas.
There is a need for a multilayer record carrier suitable to be scanned by means of a single scanning head and provided with control information, i.e. information which can be used for reading and/or writing user information in the record carrier. The control information may comprise general data about user information, such as the name of manufacturer of the record carrier, the author of the stored user information, data about encryption, maximum radiation power during writing, reading and/or erasing, and reallocation tables. The control information may also comprise a table of contents indicating the locations in an information area where given parts of the information are stored.